The development and innovation in the field of wind turbines in recent decades has resulted in increasing the size and power of wind turbines thus leading to an increase in the dimensions in height and diameter of their supporting towers.
Hybrid towers formed by a set of concrete segments in the lower part and one or more metal segments in the upper part are one the tower architectures suitable to meet these requirements.
For connecting a metal segment to a concrete segment the most commonly used solution is probably using prestressed steel bars 5 arranged in a widened area 13 of the upper end of the concrete segment 11 fixed to an anchoring plate 7 by nuts 8 (see FIGS. 1a and 1b). Once the construction of the concrete segment 11 is completed, the prestressed steel bars 5 are embedded in the concrete of said widened area 13 with projecting ends arranged to serve as attachment means with the base 17 of metal segment 15 together with nuts 9.
In a variant of that solution anchoring plates 7 are not embedded in the concrete of the widened area 13. Among its disadvantages the following should be noted:                Prestressed steel bars 5 have to be placed one by one with the difficulties that entails taking into account the situation in height of concrete segment 11. It slows down the mounting process.        A platform for access to the anchoring plates 7 of prestressed steel bars 5 is required.        The maximum tolerances for the correct positioning of the prestressed steel bars 5 are great. Relative displacements between the ducts during concreting can occur.        In case of on-site concrete towers, the assembly process is severely penalized.        
In another variant of the solution aforementioned anchoring plates 7 are embedded in the concrete of the widened area 13. Among its disadvantages the following should be noted:                It is more difficult to ensure the correct positioning of the prestressed steel bars 5. Relative displacement between them can occur during concreting.        In case of on-site concrete towers, the assembly process is severely penalized.        
The present invention is directed to solving these problems.